Oral administration of a single high dose or repeated low doses of protein has been shown to induce systemic unresponsiveness, presumably in the presence of mucosal IgA antibody responses (Challacombe et al., J. Exp. Med. 152:1459-1472, 1980; Mestecky et al., “The mucosal immune system.” In Fundamental Immunology. Paul, ed. Lippincott Williams & Wilkins, Philadelphia, Pa., 965-1020, 2003). In earlier studies, this type of immune response was dubbed oral tolerance and the concept was used to refer specifically to immune responses elicited in mucosa-associated as opposed to systemic lymphoid tissues (Tomasi, Transplantation 29:353-356, 1980). However, previous studies showed that tolerance induction occurred in the mucosal effector lymphoid tissues (Kato et al., J. Immunol. 166:3114-3121, 2001). Thus, mice fed large amounts of ovalbumin (OVA) prior to oral challenge with OVA plus native cholera toxin (CT) as mucosal adjuvant exhibited antigen (Ag)-specific unresponsiveness in both systemic and mucosal compartments, while those fed PBS showed high levels of secretory (S)-IgA Ab responses (Kato et al., J. Immunol. 166:3114-3121, 2001).
This unique response is an important natural physiological mechanism whereby the host presumably avoids development of hypersensitivity reactions to many ingested food proteins and other antigens (Garside et al, Gut 44:137-142, 1999). Thus, tolerance (or systemic unresponsiveness) represents the most common response of the host to the environment. In addition to showing tolerance to several thousand different food proteins, the host tolerates indigenous microflora which colonize the large intestine. Further, the development of mucosal tolerance against pollen and dust antigens could also be essential for the inhibition of allergic reactions, including IgE-mediated hypersensitivity. Indeed, tolerance is so strong that oral immunization only succeeds in inducing mucosal and systemic immunity when potent mucosal adjuvants, vectors or other special delivery systems are employed (Fujihashi et al, Acta. Odontol Scand. 59:301-308, 2001).
It is now generally agreed that oral tolerance is established and maintained at the level of T cells (Holt, Allergy 53:16-19, 1998; MacDonald, Curr. Opin. Immunol. 10:620-627, 1998; Mayer, Clin. Immunol. 94:1-8, 2000; Strobel & Mowat, Immunol Today 19:173-181, 1998; Strober et al., J. Clin. Immunol. 18:1-30, 1998; Wardrop & Whitacre, Inflamm. Res. 48:106-119, 1999; Weiner et al., Annu. Rev. Immunol. 12:809-837, 1994). Recent studies have identified dendritic cells as key players in the direct or indirect (via T cells) induction of oral tolerance (Mowat, Nat. Rev. Immunol. 3:331-341, 2003; Kato et al., Int. Immunol. 15:145-158, 2003; Nagler-Anderson & Shi, Crit. Rev. Immunol. 21:121-131. 2001; Viney et al., J. Immunol. 160:5815-5825, 1998; Williamson, J. Immunol. 163:3668-3675, 1999; Weiner, Immunol Rev. 182:207-214, 2001). Though the precise mechanisms by which oral delivery of Ag elicits a state of systemic unresponsiveness are not fully understood, the dosage of Ag has been shown to be an important factor (Friedman & Weiner, Proc. Natl. Acad. Sci. (USA) 91:6688-6692, 1994). For example, a high oral Ag dose leads to T cell clonal deletion or anergy, which is characterized by inhibition of both Ab- and cell-mediated immune (CMI) responses (Melamed & Friedman, Eur. J. Immunol. 25 23:935-942, 1993; Whitacre et al., J. Immunol 147:2155-2163, 1991; Chen et al., Nature 376:177-180, 1995). On the other hand, repeated delivery of low doses of protein induces cytokine-mediated active immune suppression characterized by the presence of regulatory T cells, which include TGF-β-producing Th3 cells and IL-10-producing T regulatory one (Tr1) cells or CD4+ CD25+ T regulatory (Treg) cells (Chen et al., Science 265:1237-1240, 1994; Groux et al., Nature 389:737-742, 1997; Nagler-Anderson et al., Nat. Immunol. 5:119-122, 2004). Regulatory-type T cells were first rediscovered as acquired-type Tr1 cells playing a central role in suppressing inflammatory bowel disease development (Groux et al., Nature 389:737-742, 1997). Acquired-type Treg cells, which differentiate from naïve T cells, regulate tolerance to food Ags, bacterial flora and pathogens by producing suppressive cytokines such as TGF-β1 and IL-10 (Cottrez & Groux, Transplantation 77:S12-15, 2004). In contrast, naturally occurring CD4+ CD25+ T cells or innate-type Treg cells, which are also suppressive, control the proliferation, expansion and differentiation of naïve T cells in a direct cell contact manner (Dieckmann et al., J. Exp. Med. 196:247-253, 2002) and migrate preferentially to lymphoid tissues, mainly the spleen (Cottrez & Groux, Transplantation 77:S12-15, 2004).
In addition to CD4+ T cell function, gut-associated lymphoreticular tissues (GALT) play critical roles in the induction of oral tolerance. In this regard, our previous studies showed that Peyer's patch (PP)-deficient (PP-null) mice generated by in utero treatment of mothers with lymphotoxin beta-receptor (LTβR)-immunoglobulin (Ig) fusion protein failed to exhibit systemic unresponsiveness to oral protein antigens (Ag) such as OVA (Fujihashi et al., Proc. Natl. Acad. Sci. (USA) 98:3310-3315, 2001). In contrast, others reported that PPs were not required for the induction of systemic tolerance (Spahn et al., Eur. J. Immunol 32:1109-1113, 2002). Recent studies have shown the importance of Ag-specific CD4+ CD25+ Treg cell clones from PPs in oral tolerance induction. Thus, Treg cells from PP of mice given a high dose of β-lactoglobulin produced high levels of TGF-β1, and adoptive transfer of these clones reduced Ag-specific plasma IgG Ab responses (Tsuji et al., Int. Immunol. 15:525-534, 2003). Despite these compelling studies, the precise cellular and molecular mechanisms and the role of PPs in the induction of systemic and mucosal unresponsiveness still remain to be elucidated.
Adenoviruses enter the host via attachment to the mucosal epithelia by its protein known as “fiber protein”. Likewise, reoviruses infect the host by attaching to M cells via a protein called “protein Gσ1” (pσ1; Wu et al., Proc. Natl. Acad. Sci. (USA) 98:9318-9323, 2001; Rubas et al., J. Microencapsul 7:385-395, 1990). These attachment proteins of adenovirus ssp. and reovirus ssp. are well known, and share a strikingly structural similarity despite lack of homology at the primary structure level. Both proteins are composed of a N-terminal shaft followed by a C-terminal globular domain, sometimes referred to as “head” or “knob”. The shaft inserts into the viral capsids, while the globular domains contain the cell-specific targeting regions. For both of these viruses, the shaft contains a domain that causes the protein to form homotrimers, the active form of the protein.
Incorporation of pσ1 into liposomes allows the latter to bind to mouse L cells and rat Peyer's patches (Rubas et al., J. Microencapsul 7:385-395, 1990), and the recombinant pσ1 is also known to bind to NALT M cells (Wu et al., Gene Ther. 7:61-69, 2000; Wu et al., Proc. Natl. Acad. Sci. (USA) 98:9318-9323, 2001). In marked contrast to results seen when DNA is given alone, immunization with DNA complexed to poly-L-lysine-conjugated pσ1 leads to elevated S-IgA and plasma IgG Ab responses (Wu et al., Proc. Natl. Acad. Sci. (USA) 98:9318-9323, 2001).
There exists a need to develop agents that can stimulate or cause tolerance in a subject to an immunogen. It is to such agents, and compositions comprising such, that this disclosure is drawn.